Endothelin-1 is produced by cultured primary rat astrocytes and is subject to autostimulatory regulation. In this study, we examine the response of these cells to stimulation by thrombin and report that endothelin-1 is released into the culture fluid in response to thrombin treatment. However, increased production of endothelin-1 is not accompanied by a concomitant increase in steady state levels of endothelin-1 mRNA as assessed by reverse transcriptase PCR, even though thrombin stimulation leads to increased turnover of phospholipid and activation of the nuclear factor AP1. Both endothelin receptor genes (ET-A and ET-B) were found to be transcribed in primary astrocyte cultures and both thrombin and endothelin-1 stimulation result in a distinct temporary decrease in ET-A mRNA. We conclude that astrocytic production of endothelin-1 may be post-transcriptionally regulated in response to thrombin stimulation. These studies suggest a role for thrombin in endothelin-1 mediated neurological processes.